A touch panel provided as an input device to an image display device usually has a film sensor member including a transparent substrate and a transparent electroconductive layer formed on this substrate (Patent Literatures 1 and 2). Known examples of the system for a touch panel include a capacitive system, an optical system, an ultrasonic system, an electromagnetic induction system, and a resistive film system. Among these, a capacitive touch panel, which picks up the change in capacitance between a fingertip and a transparent electroconductive layer to perform input, is presently becoming the mainstream of a touch panel, along with a resistive film touch panel. A glass substrate has been widely used as the substrate of the film sensor member of the capacitive touch panel. However, a resin film is recently considered as a candidate substrate in view of the thickness and flexibility of the substrate.
An image display device generally includes an optical film such as a λ/4 plate and a λ/2 plate. Various studies have been conducted on such an optical film (see Patent Literatures 3 to 8).